The principal machine heretofore used for the purposes of testing tooth or similar specimens is the so-called cross-brushing machine, designed over 25 years ago and using only linear relative motion of the brush and tooth specimen, in a single direction. As a result, the repeated cycling, for example, into thousands of cycles, results in linear grooving of the dentin or enamel, making it very difficult, and in most instances impossible, to obtain significant and uniform data, and making the system very sensitive to the orientations of the specimens in the apparatus recording the test results.
The cross-brushing machine also has the disadvantages of using spring-operated means in order to maintain pressure between the specimen and its brush. When that machine performs a large number of cycles, the spring fatigues, giving erratic pressures leading to erratic and unreliable laboratory results, depending upon the number of times the spring is cycled and used. A further problem lies in the fact that in recent months one could not obtain consistent springs for replacement. The present instrument overcomes these problems by using a scale beam type of force means to apply pressure between the specimen and its brush, which means result in maintaining the same pressure throughout the test regardless of the number of cycles, and which is not subject to the fatigue problem. The force may, as noted, be very light, if desired for certain tests such as polishing studies, or very strong, as required for abrasion evaluation. Furthermore, the means is readily and accurately adjustable.
The cross-brushing machine also has the problem that the moving members of each brush specimen pair do not move in a vertical direction, and as a result did not prevent stratification and settling in the liquid carrier of finely-divided particles of the medium being tested. This also results in unreliable and irregular results. The present instrument employs a vertically movable brush holder with an agitator that is immersed in the liquid carrier, and constantly maintains pace with the movement of the movable member in order to agitate and maintain the liquid suspension homogeneous throughout the test.
Another feature of the present invention is that each brush and specimen are maintained in an unvarying planar relationship during the movements of the brush across the specimen. This result is obtained by having the specimen move toward and away from the brush in a rigidly-maintained fore-and-aft path, at right angles to the movements of the brush. The brush holder is held firmly for movements in its plane of operation and the brush is held against any rocking or twisting movements in the holder.
The present instrument has six stations for specimens, each comprising a specimen and a brush in a slurry cup, with the scale beam means to urge the brush and the specimen together. The scale beam means, in addition to the advantages above recited, facilitate calibration of the brush pressures which may be set individually for each station by a simple sliding adjustment of poises along the beams. The transmission apparatus for delivering the force of the scale beam to the brush-specimen interfaces is highly friction-free and the movements are horizontal in order to eliminate a need for counterbalance. The machine provides brush pressure of 100-500 grams linearly and parallel to the specimens.
There is a separable specimen clamp and a removable brush carrier for each station, so that brushes and specimens may be selected as desired for each station. As noted, the brush clamps are designed in order to insure parallelism of the brushes with their specimens during their relative movements. Each specimen is mounted on a carrier with a viseclamp that is secure, but which can be easily removed and replaced for mounting of the specimens in the vise outside the machine. The vise clamp engages the head of the brush, which is the part thereof that is flat and which can be used to assure the proper alignment of the brush and specimen.
This machine has individual slurry cups, one for each specimen. The brush holders and brushes move in a vertical plane, dip into the slurry cups, and have flexible agitators attached to the lower ends of the brush holders. The cups have sloping bottom walls that cooperate with the wiping agitators in order to insure full pickup of the material being tested and reduce or eliminate settling of the small particles which occur inherently in a polishing system. The slurry cups are of a shape to fully immerse the specimens, their holders and mechanisms in the liquid containing the material being tested. Also, there is a full length removable drip tray below the cups.
The entire mechanism is accessible, particularly the parts subject to wear. Interengaging moving parts are maintained spaced from the slurry, and particularly are above it so as to minimize gravity effect in delivering abrasive slurry to them.
This machine produces movement between the brushes and specimens in either an X or a Y direction (i.e., vertical or horizontal), or a combination of both, which avoids deep scratching caused by repeated brushing back and forth along the same parallel line. This renders the specimen, after test, insensitive to its orientation in the recording device which is used to evaluate the effects of the experimental design. The older cross-brushing machine produced rectilinear grooves all in the same direction and as a consequence, the response of the recorder which measures polishing or cleaning depends upon whether the specimen is read crosswise or lengthwise of the grooves -- i.e., the reading depends upon orientation of the specimen in the recorder. As a result, one may obtain almost any data he wishes depending upon the orientation and placement of the specimen.
The range of movement, and the speed, of the brushes are individually adjustable for each of their two directions of movement. The stroke adjustment in the vertical direction is 0-2.54 centimeters, and that in the horizontal is one-half that amount.
Count-down pre-set counting means are provided. These can be set to be controlled by the cycles of either axis. When the machine reaches the respective count, it automatically reverses the motors of both axes until the machine is centered at its starting positions for both axes, after which it stops. It then can be restarted by resetting the counter, assuming the appropriate manual switches are closed.
The control may thus be effected by counting either the X-axis or the Y-axis cycles, as desired by the operator, or the present counter may be manually bypassed and the machine operated by manual control.
A calibration circuit is provided in order to enable the speed to be calibrated with respect to the dials.
Other features than those described above will appear from the full description which is to follow.